This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Ebola virus (EV) causes hemorrhagic fevers in humans with a high mortality. Although significant research effort have benapplied to understand the mechanism of viral infection, and more specifically the mechanism of viral fusion into the host cell, it remains unrevealed. It is known, to date, that EV shares the common properties of viral fusion: A single surface transmembrane glycoprotein (GP), belonging to class I viral fusion proteins plays a central role in the entry into the target cells by mediating the merging and fusion between the viral and the host cell membranes. The Ebola GP, expressed as a single-chain precursor, is cleaved posttranslational into two disulfide linked fragments GP1 and GP2. A specific feature of EV is the internal fusion peptide (IFP) located in the GP2 domain, containing approximately sixteen uncharged hydrophobic residues (residues 524 [unreadable]539) that is typical for a family of viral fusion peptides. It is thought that in the fusion active state the GP2 protein inserts its intrinsic FP into the membrane of the target cell and this is a critical stage in the fusion process. Despite what is available from the literature, there is no complete understanding of the EV fusion mechanism. Moreover, in contrast to N-terminal fusion peptides, generally the internal fusion peptides are poorly characterized in their interaction with membranes and possible structural role. In regard to above, we have undertaken an in vitro pulsed dipolar ESR study on a synthetic peptide with the amino acid sequence GAAIGLAWIPYFGPAA, representing the naturally accruing Ebola virus fusion region, and two modifications with substituted Ala2Cys or Ala2 to Cys and Ala15to Cys. Mutations to cysteines makes it possible to attach paramagnetic spin-labels to these residues and obtain structural information by measuring distances between these spin-labels. Hence, different conformations upon binding to mimetic membranes could be determined and characterized.